That part you quoted was more directed at just regular hits, not prospects.If you are prospecting is this not just true by definition?
The vast majority of prospects, even good ones, will not work out. Thus, if they are a "big hit" they are most likely at the peak of their value and should be sold. In most cases once a prospect reaches "big hit" territory, especially, if they are still a long way from the majors, the card can only go down — or at least will experience periods where it is down from its "big hit" value.
Should you not be fading the "big hit" guys and buying guys you like, who for whatever reason (poor recent performance, injury, not a big name prospect) are not the "big hits".
(Of course, I'm not a baseball collector so actually have no idea what I am talking about!)
My prospect will probably get dumped when he gets the next promotion